This invention relates generally to magneto powered capacitive discharge ignition systems for internal combustion engines and more particularly to magneto powered capacitive discharge systems including a voltage regulation circuit for regulating the voltage developed on a charge capacitor utilizing a high power silicon bilateral voltage triggered switch.
Typical prior art regulator circuits utilized in magneto powered capacitive discharge ignition systems have employed SCR or transistors tirggered by zener diodes, or employed one or more series connected zener diodes connected directly in parallel with the charge capacitor. Ideally, these regulator circuits prevent overcharging of the charge capacitor by limiting the magnitude of the voltage at the positive terminal of the charge capacitor to the zener diode breakdown voltage. The components of such voltage regulator circuits, however, are subject to high power dissipation and failure due to component tolerance and excessive voltage on the charge capacitor, or due to high magnitude voltage and current surges occurring during discharge of the charge capacitor through the primary winding of the ignition coil.
Another typical prior art voltage regulator circuit uses a zener diode connected in parallel across the magneto charge coil upstream of a blocking diode. The zener diode in this arrangement limits the positive voltage output of the magneto charge coil to the zener diode breakdwon voltage, but shunts the negative output of the charge coil, thereby undesirably reducing the speed at which the charge capacitor charges, and consequently, a magnitude of the voltage developed thereon. Further, the zener diode in such circuits is subject to excessive magneto charge coil voltage, due to component tolerance, or due to an open circuit fault in the ignition triggering SCR or the primary winding ignition coil circuits. As a result of such excessive voltage, the zener diode is subject to excessive power dissipation and consequent failure.
Another type of ignition system voltage regulator circuit known in the art utilizes a triac and varistor circuit connected in parallel with the charge capacitor to prevent overcharging of the charge capacitor. In this type of circuit, the varistor is connected to one end terminal of the charge coil and the other terminal is connected to the gate of the triac. The varistor is rendered conductive and applies a trigger current pulse to the triac gate rendering the triac conductive in response to a voltage on the charge capacitor exceeding a predetermined value. This triacvaristor circuit configuration is subject to component failure of both the triac and the varistor, requires multiple components to perform the switching function, and fails to provide a high degree of accuracy of regulation.
Thus, all of these prior art voltage regulator circuits utilized in magneto powered capacitive discharge ignition systems have been subject to voltage regulator component failures and hence have proven insufficiently reliable. Particularly, the semiconductor devices in such circuits are subjected to high voltages and currents which result in failure due to the power dissipated in the device or due to high voltage breakdown. In addition, these components have not provided consistent, accurate regulation thereby subjecting other circuit components to excessive voltages leading to increased failure rates. The failure of such prior art voltage regulator circuits has been particularly serious and troublesome because it results in the failure of the ignition system, and more importantly, because it results in the failure of the internal combustion engine and the vehicle in which the ignition system controls. Such voltage regulator failure requires an annoying and costly replacement or repair of the voltage regulator circuit before the ignition system and hence, the internal combustion engine and vehicle, can again be made operative.